This project is composed of two major areas of research: (1) studies of pyrimidine nucleotide synthesis in vivo and (2) cellular control of nucleoside diphosphate hexose synthesis and glycosaminoglycan production. In a continuing study of the biochemical effects of low-dose PALA (currently undergoing clinical evaluation as a biochemical modulator of 5-FU metabolism) we found marked differences in tissue sensitivities in the intact mouse: hepatic de nvo pyrimidine synthesis is exquisitely sensitive and is completely inhibited by low-dose PALA (50 mg/Kg) for at least 96 hours, whereas intestinal synthesis is transiently inhibited by high dose PALA (400 mg/Kg) and actually stimulated by low-dose PALA. These data suggest that low-dose PALA might decrease 5-FU intestinal toxicity and support a role for the intestine as a source of circulating uridine when hepatic synthesis and export are inhibited. Studies have also focused on the cellular regulation of hyaluronan synthesis as a target to control the invasive and metastatic properties of malignant cells. Hyaluronan production by intact Swiss 3T3 fibroblasts was characterized with regard to size, rates of elongation and release from cells, and the effect of protein synthesis inhibitors. These data, along with comparable studies using isolated membrane preparations, suggest a novel mechanism of cellular control of hyaluronan synthesis: one hyaluronan synthetase molecule is responsible for the synthesis of one hyaluronan chain. In an effort to elucidate regulatory pathways involved in the control of hyaluronan synthesis, compounds that inhibit specific pathways were studied for their effect on hyaluronan synthesis. Inhibitors of eicosenoid metabolism, specifically mefenamic acid and indomethacin, were potent inhibitors of hyaluronan synthesis but did not inhibit DNA synthesis, indicating that the regulation of hyaluronan synthesis is separable from DNA synthesis. In addition, arachidonic acid activates hyaluronan synthesis in serum-free media.